There has been a rapid progress in thin film transistor liquid crystal display (TFT-LCD) in the past few years. Although picture quality of a LCD (liquid crystal display) from front view might be great, the color might change if viewed from the side. Therefore wide viewing angle technologies become popular for reducing the color change upon viewing from the side. Advanced super dimension switch (ADSDS) is one of the wide viewing angle technologies recently developed to meet the requirements of a large screen high definition LCD for desktop and TV. In ADSDS technology, a multi-dimensional field is formed using a field formed by edges of the slit electrodes within a same plane and the field formed between the slit electrode and a plate electrode, causing rotations of liquid crystal molecules in any orientations within the liquid crystal cells between the slit electrodes and right above the electrodes, thereby increasing operation efficiency of the liquid crystals as well as improving the light transmittance. By ADSDS technology, display quality of a TFT-LCD can be improved with various advantages including high resolution, high transmittance, low power consumption, wide view angle, high aperture ratio, low chromatism, and no push mura etc.
As shown in FIG. 1, an ADSDS LCD panel comprises a color filter substrate 12 and an array substrate including a lower transparent ITO common electrode 3′ (Vcom, may be in the form of a plate electrode) formed on a substrate 1 and an upper strip electrode 8′ (may be formed as slit electrodes) as pixel electrode on a passivation layer 7. The strip electrode 8′ is formed by processes such as exposure, development, etching and lifting off etc. Lights are allowed to pass through most part of a color filter substrate 12 and the array substrate with the multi-dimensional field formed therebetween, thereby achieving a wide viewing angle with high brightness. It is noted that the transmittance of the ADSDS LCD panel is associated with pitch a of strip electrode 8′.
In the ADSDS LCD panel, the pitch a of the strip electrodes is equal to a sum of a width (CD) b of a strip electrode and a spacing c between adjacent strip electrodes. In order to ensure a good brightness of the LCD panel, if the pitch a of the strip electrode is 10 μm, the width b of the strip electrode is 4 μm, and the spacing c between the electrodes is 6 μm; and if the pitch a of the strip electrode is 8 μm, the width b of the strip electrode is 2.6 μm, and the spacing c between the strip electrodes is 5.4 μm. An excellent brightness of the LCD panel may be achieved in case that the pitch a of the strip electrode is 6 μm, the width b of the strip electrode is 2 μm, and the spacing c is 4 μm. However, since a width limit that a conventional exposure apparatus may expose is in a range of 3-5.0 μm, it may be difficult to achieve a width b of the strip electrode less than 3 μm in reality. In addition, defects including mura or spots might occur due to width variation of the strip electrodes, thus decreasing display quality of the LCD panel.
FIG. 2 shows the relationship between the transmittance of the LCD panel and the width b of the strip electrode. As the pitch a decreases, the brightness (i.e., transmittance) of the LCD panel increases. Despite of the increased brightness, the process window for maintaining a uniform brightness is decreased.
FIG. 3 shows a simulation of transmittance variation vs a variation of width b of the strip electrode. The two curves in FIG. 3 represent a case with a pitch a of the strip electrode of 8 μm and a case with a pitch a of 10 μm, respectively. It can be seen that in case of identical increase percentage of the width b, the transmittance changes more in the case with the pitch a of 8 μm than that in the case with the pitch a of 10 μm, thereby the former is more likely to cause defects such as spots or mura.
It may be known from FIG. 2 and FIG. 3 that the smaller the pitch a of the strip electrode, the better the brightness of the LCD panel is, and if the pitch a of the strip electrodes is the same for all strip electrodes, the smaller the width b of the strip electrode is, the better the brightness of the LCD panel is.